Environmental Synthesis & Communication | It’s Getting Hot in Here: Climate Change Experiment Finds Unexpected Consequences for New England forests

This year has once again brought us some crazy weather: snow in October. Although the saying, “if you don’t like the weather in New England just wait a minute,” holds true, this much snow in October is definitely out of the ordinary. The last time Boston received this much snow (3.5”) in October? 1872. While unexpected weather events are common in New England, their increasing frequency is a symptom of climate change.

Climate change is no secret—our world is getting warmer as a result of human introduction of greenhouse gases to the atmosphere. But the havoc climate change will wreak on various ecosystems is complex and often not well understood.

A new study published in Ecology this summer looks at the potential impacts of both warmer growing seasons and decreased winter snowpack on New England’s northern hardwood forests. This study (Climate Change Across Seasons Experiment or CCASE) uses forest plots with manipulated precipitation and temperature to simulate future climate scenarios at the Hubbard Brook Experimental Forest. Located in the White Mountains of New Hampshire, Hubbard Brook is one of the most important sites in the northeast for ecosystem ecology research.

Study design of the manipulated climate variables and plots at the Climate Change Across Seasons Experiment. Figure by Pamela Templer.

As the study points out, climate models for the Northeast over the next century predict warming temperatures, changing precipitation patterns, and even more unpredictable weather. Our snowy Halloween is just another reminder that those erratic changes are already here.

On the surface, warmer winters probably sound appealing: less bitter cold days when the wind bites through your jacket, fewer wintry mornings freezing your fingers while scraping snow off your car. But changing winters is going to change a lot more than just the snow.

Less winter snowpack means less snow on the ground. Snowpack acts like insulation for fine tree roots, so less insulation leads to more damage. Surprisingly it is these tiniest tree roots, known as fine roots, that are most critical for the future ability of trees to take up water and nutrients. Damage on a local scale can have drastic implications for water and carbon movements of New England forests on a broader level.

Thermal cables on the forest floor that provide the artificial warming for the experimental plots of the CCASE experiment

Unfortunately, warming summer temperatures will not increase the carbon storage capacity of northern hardwood forests. Although the study did find that soil warming alone caused plants to grow faster and thus intake more carbon, this was offset in plots with more frequent soil freezing as the damage to plant roots reduced their ability to grow faster. These results cast doubt on whether northern temperate forests will continue to be a carbon storage space as climate change worsens. This would only speed up the feedback loop of climate change impacts.

The CCASE study also found that changes in soil temperature over the next century will impact the water cycle. On average, a single mature oak tree pumps 100 gallons of water into the atmosphere each day. Trees essentially control the water cycle in northern hardwood forests. When considering an entire forest, this pumping accounts for two-thirds of all water movement in the ecosystem. This research suggests that ecosystems are going to change dramatically in a warmer climate, cranking up that pump by 42 to 61 percent. Increased water uptake during the growing season could exacerbate water-stress for forests, particularly with the concurrent rise in frequency of droughts.

These findings spell disaster for two New England traditions: colorful foliage and maple syrup.

Drought stress on trees can drastically shorten the fall foliage season. Colorful foliage is typically triggered by the cooler days and longer nights of fall. Moderate heat and drought can prolong this process, giving us particularly vibrant fall colors. Extreme drought and high heat, like the conditions occurring in New England this year, cause color changes to happen sooner and faster. Trees that are mildly stressed by drought and heat will delay changing color and dropping their leaves, but when trees are severely stressed by weather conditions, the process accelerates. What is a New England forest without its changing leaves? For many communities, it is not just the loss of a beautiful view, it is the loss of tourism.

The maple syrup industry is under similar stress from the combined loss of deep snowpack and increasingly unpredictable early spring weather. Sugar maples are particularly susceptible to damage to fine roots from soil freezing. Maple sugaring is dependent on the combination of below-freezing nights and above-freezing day temperatures. Climate change is pushing this timing earlier and often shortening the length of the season, mirroring changes to the fall foliage season.

Although the scientists look specifically at red maple trees, they conclude that the changes in climate will have broader implications for the future of northern temperate forests as a whole. These climate changes certainly mean a more unpredictable world—random October snow storms may be the new normal. So, as harmless as warmer weather and less snow might sound, it could mean the end of the New England forests we know and love.

For more information on the Climate Change Across Seasons Experiment look here:

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